A handover is a process of transferring an ongoing wireless connection of a wireless device from a serving access node to a target access node to provide a transparent service for mobile users. Handover is important in a wireless network for mobility management function.
Generally, a handover procedure is based on a downlink signal quality measurement, which is schematically shown in FIG. 1. It is illustrated that an access node is serving for a wireless device in a wireless network. In order to make a handover decision, the access node transmits the wireless device a downlink measurement control signaling, from which the wireless device could obtain downlink signal quality measurement control parameters, such as a carrier frequency, a measurement bandwidth, measurement object, and measurement reporting configuration. According to configuration of downlink measurement control signaling, the wireless device performs a downlink signal quality measurement for a plurality of access nodes, and then transmits a downlink signal quality report to the access node serving for the wireless device. Then, the serving access node makes a handover decision according to the downlink signal quality report and transmits a handover command to the wireless device. In multiple antenna cellular systems, a plurality of beams will be exploited to improve signal quality, while continuously transmitting downlink reference signals in all these beams is not desirable, since it will generate a lot of interference and increase energy consumption for the access node. Moreover, in the downlink measurement based handover procedure for multiple beam communication system, a wireless device has to measure a plurality of downlink reference signals in a plurality of beams and then it needs to report all these measurement results to a serving access node, which takes more time to perform a handover procedure. Therefore, the downlink measurement based handover procedure is less desirable especially in multiple beam communication systems.